I’m looking for advice and/or actual knowledge regarding the maximum exhaust that can effectively be installed on an Evo using the stock turbo w/ the following mods:
BC 280 int/272ext cams, O2 housing & headers, 2.75” Tanabe DP, full 3” exhaust w/ Magnaflow, Injen intake w/UICP, GFB BOV, Walbro 255, MBC, (32”x3”x12” FMIC to be installed and re-tuned) custom street tune(rich= 10.0-10.5 @ WOT)
I’ve done some modifications on my F250 SD 7.3 TD. The larger the exhaust, the less heat build up and the faster the turbo spools. Would you actually feel or notice any worthwhile benefits with a 3” DP & a full 3.5” exhaust? Do you actually want any backpressure or is it like the TD’s ? Wouldn’t it allow the turbo to spool faster, get rid of heat quicker, thus more easily creating boost and possibly dropping the cold air charge?
Would it produce more torque? Please, only real info or experience, not “guess-timates”unless it's based on knowledge.

 

You won't see any difference in power/torque/spool up. Please do a search on http://www.dsmtuners.com to confirm what I have said.

 

Thanks for the reply, but I'm not interested in searching on their board, as there are plenty of knowledgable people here. If you have a direct link you'd like to post that would be fine.
As I understand it, backpressure & heat are the turbos two worst enemies, therefore anything that can be done to eliminate and/or minimize them would benifit. The question is, where does one draw the line. A 3.5" would definately eliminate more BP. How much & at what cost VS benifit is the question?
I just did a search on yahoo and read several articles that address these very issues, one on a Buick Grand National site and the other on a turbo diesel site. It seems that a turbo works best with the least amount of BP possible, whereas a NA engine requires it. All the Grand Nationals and turbo diesels that are going "***** out", and many severe duty race cars have very short & large diameter downpipes. I would venture to say that if you made a pass down the 1/4 w/out your exhaust attached to your DP, you would notice an appricable difference.
So I'm not presently buying your reply that it would produce no benifit in said areas, unless you can substantiate your theory.
But thanks anyway.

 

Better flow, I would assume. I hardly see Supra guys using 3 inch exhausts. Its always 3.5 and some cases 4. Now these are high powerd supras 600+whp. This leads me to think that the bigger the exhaust more flow less back pressure= more topend power?

 

with a downpipe of only 2.75 would it make that much of a difference in backpressure?

 

I think you'd need to be running a pretty large turbo, or more than 2.3 liters of displacement for 3" to be a restriction where a 3.5" exhaust would make that much of a difference. Given the opportunity I would run a 3.5" exhaust, but I don't think there would be much of a performance gain. Heck, I have a supercharged 383cid malibu (6 liters) running dual 3" exhaust, that means 3 liters of exhaust volume are able to pass through each pipe, if that car is doing well with it, I would doubt the 2.0 with most turbos would have any trouble.

 

You might receive .5 horsepower. Do a dyno run with 3 inch exhaust. Then do a dyno run with NO exhaust. The difference will be 5-10hp. Adding another 1/2 inch of exhaust isn't going to do jack **** except annoy the hell out of your neighbors and other drivers. Also please note, a high flowing exhaust stream usually means LESS bottom end torque but increased top end. Not that a 3.5 inch would even do anything, unless you were over the 1000hp range like John Shepard (runs a 3.5 inch).

 

Plus, that would be quite an expensive upgrade not to mention have clearance issues. The same increase of volume and flow would probably be needed on the other end too.

 

If you're not running enough boost, you will lose back pressure which in turn will cause you to lose low end torque.

 

I'm not sure that loss of DP = loss of torque, in fact, I would think exactly the opposite. If a turbo reaches full spool faster, that means your in the powerband faster. correct me if I'm wrong.

 

i might be wrong or half right but didn't sheppard gain like 3-5 mph on his trap speed when he switched from 3in to 3.5 in? I'm not saying that you should expect a gain like that i just thought that was impressive!

 

well you have to look at the fact of the stock turbo also..... the O2 housing diameter needs to be alot larger to get the full benefits of a larger exhaust, sure you will gain power from a 3" turboback exhaust, but the weakest link is the O2 housing. So upgrading to 3 1/2 " or 4" exhaust from a 3" setup you wont see much power increase.

 

For yours and everyother normal Application, i dont see the point of going to a 3.5. Thats a little nuts. However if you plan on pushing more then 600whp i supose its a good idea.


im sure your correct and it wouldnt surprise me. But shep was running Some Crazy huge turbo as well...... So Yes in the case you might be running a 42-45r, i dont see the point......

The Famous Black Evo From AMS was running a 3in TBE with the AMS kit and he was running over 600+ to the wheels..... So Ya, they only upgraded when he was making 800whp+ So for a company to make a 3.5 TBE, i think its a little over the top.

 

I think bigger is better personally. ive seen some gains with supra (only real comparison with different size exhaust) even at low boost 450whp going from 3" to 3.5 then to 4". Any turbo car will benifit from a larger exhaust. is it needed probably not. i say if ur shopping. go for it if you can find one. the APS one is almost never instock in country. the only down side i see is clearnce issues.

As far as "no back pressure will hurting your tq" that statment is dead wrong on a turbo car.

 

the bigger the better no doubt, but 3.5" vs. 3" may save you very little in the backpressure department, hardly noticeable until your making big power (600+), and have a lot of exhaust to deal with. You need to know a/f ratio, a fuel flow rate, EGT's and you can calculate the volume of exhaust you are generating, and from there estimate backpressure caused by your individual setup. I'm sure there are some "estimates" out there on the web based on hp, just have to find them.

For all you noobs, any backpressure AFTER the turbo is bad, bad, bad. You do not lose torque by going bigger after the turbo.